Django GenericForeignKey Null

Django GenericForeignKey provides a way to create a relation between any two models without explicitly defining a foreign key constraint in the database. It uses content types framework to create a relation between models.

In some cases, you may not want to enforce the foreign key constraint and allow the relation to be null. This can be achieved by setting the null=True parameter on the GenericForeignKey field.

Example

Let's say we have two models Model_A and Model_B:

from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
from django.db import models

class Model_A(models.Model):
    name = models.CharField(max_length=100)

class Model_B(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

By default, content_object field would not allow null values. To allow null values, we can modify Model_B as follows:

class Model_B(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id', null=True)

Conclusion

In conclusion, if you want to allow the relation between two models to be null, set null=True parameter on the GenericForeignKey field. This will allow the field to store None as a value.